New data on γ → p → → η p with polarized photons and protons and their implications for N ??→? Nη decays

摘要

The polarization observablesT,E,P,H, andGin photoproduction ofηmesons off protons are measured for photon energies from threshold toW=2400MeV (T), 2280 MeV (E), 1620 MeV (P,H), or 1820 MeV (G), covering nearly the full solid angle. The data are compared to predictions from the SAID, MAID, JüBo, and BnGa partial-wave analyses. A refit within the BnGa approach including further data yields precise branching ratios for theNηdecay of nucleon resonances. ANη-branching ratio of0.33±0.04forN(1650)1/2?is found, which reduces the large and controversially discussedNη-branching ratio difference of the two lowest massJP=1/2?-resonances significantly.